//jQuery.fn.extend({
//	autoHeight: function() {
//		return this.each(function() {
//			var $this = jQuery(this);
//			if(!$this.attr('_initAdjustHeight')) {
//				$this.attr('_initAdjustHeight', $this.outerHeight());
//			}
//			_adjustH(this).on('input', function() {
//				_adjustH(this);
//			});
//		});
//		/**
//		 * 重置高度 
//		 * @param {Object} elem
//		 */
//		function _adjustH(elem) {
//			var $obj = jQuery(elem);
//			return $obj.css({
//				height: $obj.attr('_initAdjustHeight'),
//				'overflow-y': 'hidden'
//			}).height(elem.scrollHeight);
//		}
//	}
//});

/**
 * 文本框根据输入内容自适应高度
 * {HTMLElement}   输入框元素
 * {Number}        设置光标与输入框保持的距离(默认0)
 * {Number}        设置最大高度(可选)
 */
var autoTextarea = function (elem, extra, maxHeight) {
    extra = extra || 0;
    var isFirefox = !!document.getBoxObjectFor || 'mozInnerScreenX' in window,
    isOpera = !!window.opera && !!window.opera.toString().indexOf('Opera'),
        addEvent = function (type, callback) {
            elem.addEventListener ?
                elem.addEventListener(type, callback, false) :
                elem.attachEvent('on' + type, callback);
        },
        getStyle = elem.currentStyle ? 
        function (name) {
            var val = elem.currentStyle[name];
            if (name === 'height' && val.search(/px/i) !== 1) {
                var rect = elem.getBoundingClientRect();
                return rect.bottom - rect.top -
                       parseFloat(getStyle('paddingTop')) -
                       parseFloat(getStyle('paddingBottom')) + 'px';       
            };
            return val;
        } : function (name) {
            return getComputedStyle(elem, null)[name];
        },
    minHeight = parseFloat(getStyle('height'));
    elem.style.resize = 'both';//如果不希望使用者可以自由的伸展textarea的高宽可以设置其他值

    var change = function () {
        var scrollTop, height,
            padding = 0,
            style = elem.style;

        if (elem._length === elem.value.length) return;
        elem._length = elem.value.length;

        if (!isFirefox && !isOpera) {
            padding = parseInt(getStyle('paddingTop')) + parseInt(getStyle('paddingBottom'));
        };
      scrollTop = document.body.scrollTop || document.documentElement.scrollTop;
      
        elem.style.height = minHeight + 'px';
        if (elem.scrollHeight > minHeight) {
            if (maxHeight && elem.scrollHeight > maxHeight) {
                height = maxHeight - padding;
                style.overflowY = 'auto';
            } else {
                height = elem.scrollHeight - padding;
                style.overflowY = 'hidden';
            };
            style.height = height + extra + 'px';
            scrollTop += parseInt(style.height) - elem.currHeight;
            document.body.scrollTop = scrollTop;
            document.documentElement.scrollTop = scrollTop;
            elem.currHeight = parseInt(style.height);
        };
    };

    addEvent('propertychange', change);
    addEvent('input', change);
    addEvent('focus', change);
    change();
};